1. Field of the Invention
The present invention relates to a guide apparatus for a cam ring which has an inner cam groove in which a cam pin of a movable member is fitted, so that when the cam ring rotates, the movable member is moved in a predetermined direction.
This application is related to commonly assigned application U.S. Ser. No. 07/616,260, the disclosure of which is expressly incorporated by reference herein.
2. Description of the Related Art
A cam ring guide apparatus as mentioned above is widely used, for example, as a lens guide apparatus in a zoom lens. Namely, a lens holding frame which holds a lens group has a cam pin which is fitted in a cam groove of a cam ring, so that the rotation of the cam ring causes the lens holding frame to move in the optical axis direction thereof. In a recent cam ring guide apparatus, the cam groove is formed as an inner cam groove which has a bottom wall. A cam pin is continuously biased to outwardly project from the lens holding frame in the radial direction, so as to ensure the engagement of the cam pin and the inner cam groove.
In a known cam ring guide apparatus, in order to bias the cam pin outwardly, a compression spring is provided in a cam pin supporting hole in which the cam pin is inserted. Upon assembly, after the compression spring is inserted in the cam pin supporting hole, the cam pin is pushed into the cam pin supporting hole while compressing the compression spring. Then, the lens group is fitted in the cam ring while registering the cam pin with the inner cam groove. However, these operations are troublesome and require high skill by camera manufacturing. Accordingly, for example, a beginner tends to fail to fit the cam pin in the inner cam groove, so that the cam pin comes out or is ejected from the cam pin supporting hole by the compression spring, resulting in the loss thereof.